One person was missing, but police did not know if the worker was trapped or had escaped. Search crews with dogs were looking through the rubble.

Misty Skipper, a spokeswoman for Mayor John Peyton, said early searches had turned up nothing, but they would continue until searchers were certain that nobody was trapped.

Twelve men and one woman were transported to Shands Jacksonville, hospital spokeswoman Kelly Brockmeir said. Two were in serious condition, 10 were in good condition and one was in fair condition. Some of those in good condition have left the hospital.

Susan Barrow, a spokeswoman for Baptist Medical Center, said they had three patients, but two have been released and the other is in good condition. St. Vincent's Medical Center spokesman Erik Kaldor said it also received three injured workers; one was admitted in fair condition, another was treated and released and a third was still being evaluated.

Other workers were treated at the scene.

The collapse occurred as workers were pouring concrete on the sixth floor of the garage for a condominium complex, which is located across the street from the Jacksonville Sheriff's Office.

``I heard a crack, and then it just crumbled,'' Rick Caldwell, a construction worker, told The Florida Times-Union.

Mayor John Peyton said at a news conference that the collapse occurred at shift change when workers were arriving and leaving work, so officials are checking to make sure no one else is missing.

The Occupational Health and Safety Administration is investigating the collapse.